Acid recovery process



May 11, 1948.

J. H. A. P. L. VAN D ER VALK ETAL.

ACID RECOVERY PROCESS original Filed March 29, 1941 mums@ +0:

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mrc: coruano mom PS Tluuu Nom inventors: Johannes HAR-Lanqzn van der Valk Jan D, Rugs bg wir Anomzq: ,M gankgn'n Patentecl May 11, 1948 U N-I'TED .S OFFICE 2,441,521V Y y ACID RECOVERYPROCSS Johannes H. A. P.`Langen van der Valk, Surbiton,

England; and'J an D. Ruys, Berkeley, Calif., assignors' gto vShell Development Company; San Francisco; Cali-f., a'corporaton of Delawarek Continuation of application Serial No! 385,900;- March/ 29,1941. This application August 11, 1944.` Serial No; 5492888 c Claims'. (C1: .z3-@173i This invention relates to the treatment ofinorganic acids' whichI havel become contaminated with organic impurities' :and particularly to the revivification of inorganic acid catalysts-which have become inactivated by'reacti-on'with an'd/ or absorption of such impurities; It deals with an improved procedure whereby such .acids maybe economically recovered in a'formsuitablefor reuse as catalysts and is particularly vapplicable/'to thel recovery of :sulfuric acid' 'which 'has become ineffective asa catalyst for the 'alkylation of hydrocarbons, particularly isoparail'ins,with oleflns.

An important objectof 'the' invention is to reduce Ithev expense-involved in recovering the inorganic acid content ofV acid containingorganic impurities. Another object is to avoid loss of acid and toY eliminate operating` difficulties in the concentrationof sulfuric acid-. Still another object is to minimize undesirable decomposition of organic4 components of-Waste acid. Still another object isto provide a process particularly adapted for the-recovery of spent-alkylationacid. A'fur-` therv object is to -1 provide* a recovery process wherein sulfur' dioxide evolvedduring they sul-Y furic acidy concentration may be economically re-v covered'. Other objects-andadvantages of the invention willbe apparent from the'followingdedescription;

such'recovery. A- comm'ercially practical method has been developed vwhereby the diiiiculties due to such changes in the yacid-'may beiaVoided-"and the -recoveryvof the acid maybe made more economical andrefiicient'. Y

An important feature 1 of the-process of thefin'- vention comprises diluting the acid to be treatedr to reduce the-,concentration to` a point at which undesirable*l reactionsl are substantially supe' pressed before` any "f-substantialfamount of' suchI reactionhas; taken? place and i under vconditions at whichI suchreactions aresubstantiall'y avoided during. dilution'.- Dilutions witnsteam and'water'f have' been used in the recovery of sulfuric lacid from acid sludges such, for example, as are'obtained. in the renin'g of petroleum, etc. I-Iovv-y ever, .not only hassuch 'dilution usually been 'carried `out after reactions in the `acidv have been a1'- lowed to progress to a detrimental extent but also noattempth'as been'ma'de to control the dilution conditions' 'sos as to minimizeundesirabl'e reactions during dilution. In fact, heating or other treatment leading to undesirable reactions duringv dilution has beencustomary. In view of th'fa'ct that decomposition' of organicr impuri- 'ties` followed such dilution,l it can be understood wl'fy it has not' been regarded' as ofir'nportan'ce` Whether or not'd'ecomp'osition took place before, during or after' dilution' and why the advantageousincreasedyield andimproved'ease of acid recovery obtained `by'supp'ressing undesirable reacticns'before and during the dilution step of the invention were not realized before;

Inv order'toA make th'e"inventi`on clear it Will beV describedin detail 'with particular reference tothe'recoveryof sulfuric'acid which has been used as a catalyst Vfor the-a'lkyl'atio'n' of isoparafn's by oleiins as described,rfor example, in co-y pending applicationsY Serial No. 150,544, filed June'26, 1937', and Serial No. 276,062, filed May 2'7,v 1939, now U; Si Patent No. 2,341,487. This application of the invention has been chosen as an illustration because it represents a particularly diflicult acid recovery problem and also -becausek it has-beenfound,v unexpectedly, that hydrocarbonshaving valuable drying properties may be obtained fromv spent alkylation acid by theprocess ofthe invention. To be'eiTectiv'e as acatalyst for the alkylation of' isoparafns, sulfurie acid must befofv relatively high concentrationand smallamountsof impurities inthe acidv the startingmaterialsand conditions' used in theA alkylation process and-such variablesY will-im fluence theI choice -rof "operatingv conditions which will be mostadvantageousfrfcarrying-oiit the' acidi recovery' process *off'the' invention.- In v.any case the "acidbeingl treated isY promptly diluted,

preferably under 'conditions' at v vhichsubstantial increasein'temperatureLis avoided, With-`suicient water to cause the separation of absorbedvhydrocarboniiinpurities ifi-'or'nltliel acid" and the resulting mixture is stratified or subjected to other suitable treatment for separation of the resulting phases. Such dilution is preferably carried out within about eight hours and most preferably substantially immediately after the withdrawal of the acid from the alkylation system, although longer periods may be allowed to elapse without serious loss, particularly if the acid is kept at a suitably low temperature, for example C. or below, at which no undesirable reaction takes place. Preferably the dilution is carried out with ice water or the like so as to avoid rise in temperature during dilution. Too high dilution is undesirable, because it leads to increased expense in subsequent reconcentration., For maximum separation of hydrocarbon impurities, dilution with such an amount of water will give an acid layer of about 35% to about 60%, preferably about 40% to 55%, is preferred although less dilution may be used especially where a suitable solvent for the hydrocarbons, such for example as a non-reactive hydrocarbon, as phenols or the like, is employed. Under suitable conditions 90 to 95% or more of the organic content of spent alkylation acid may be recovered as useful hydrocarbon.

The separation of hydrocarbon from dilute acid may be effected in any suitable manner. Stratification and de-cantation or centrifugation or the like may be used. If the dilution step has been properly carried out, prompt separation is not essential but as exposure of the hydrocarbon to the air leads to resiniflcation of the constituents having drying properties, it is desirable to avoid such prolonged exposure as leads to loss of yield of desired drying oil. The separated hydrocarbon may be washed, rst with water and then with a dilute aqueous base such as sodium hydroxide solution, to remove any remaining acidic bodies.

The dilute sulfuric acid remaining after the separation of the hydrocarbon is preferably reconcentrated according to the method illustrated in the acompanying gure which is a flow diagram showing the essential elements of the recovery system; for purposes of clarity pumps, heat exchangers, cooling units, bypasses, valves, vents and other auxiliary equipment have been omitted.

As described above, the spent acid is promptly diluted to about 50% concentration in the dilution and skimming unit 1 (referring to the flow diagram) from which dilute acid is continuously fed to the preliminary concentration unit i, in which a body of acid is maintained within a given temperature range as set forth hereinafter. From the preliminary concentration unit acid is continuously passed into an intermediate concentration unit 2, also containing a body of acid maintained within a given temperature range. From the intermediate concentration unit 2 acid is continuously passed through a separation unit 4 and therefrom to a nal concentration unit 3, which again contains a body of acid maintained within a given temperature range. In passing through the various concentration units the concentration of the acid is successively raised from about 50% to a value of the order of 92- 95% in the final concentration unit 3.

If, as is the ca-se where the acid is to be re-used for alkylation purposes, a concentration in excess of about 95% is desired, further concentration to 98% or more may be attained in the fortification unit 6.

The body of acid in each of the concentration units is preferably maintained within the desired temperature ranges by blowing hot gases therethrough in the known manner, the acid in preliminary concentration unit I being maintained within the range of about 1Z0-140 C., corresponding to an acid concentration range of about 67-73% H2504; in the intermediate concentation unit 2 the preferred temperature range is about 160-185 C., corresponding to an acid strength range of about Sil-%; in the nal concentration unit 3 the temperature is held within the approximate range of 21o-140 C., corresponding to acid strengths with the,- approximate range of 92-95%.

In each case the dilute acid is preferably in` troduced either directly into the body of acid in the concentration unit or may Ibe contacted with the vapors arising therefrom so as to be: preheated thereby before dropping into the bodyl of acid and at the same time precool the exit, gases. However, other suitable methods of introduction may also be used. Cottrell precipitators or other suitable types of mist separators are provided at 8a and 8b, in the gas exit lines of each of the concentration units.

Thus, in the operation of the recovery system, the spout alkylation acid is first passed to the dilution and skimming unit 1, wherein it is promptly diluted, the major portion of the hydrocarbons thereupon separating and being separately treated as previously described. Dilute acid is continuously fed from the dilution unit 'i to the preliminary concentration unit l, the body of acid therein being maintained within the aforementioned temperature range of approximately 1Z0-140 C. Thi-s temperature range is below both the foaming point of dilute alkylation acid and the point at which appreciable amounts of SO2 are evolved.l

Acid of a concentration of about 67-73% is continuously passed from l to the intermediate concentration unit 2 and into a body of acid at a tempertaure above the foaming point of the preliminarily yconcentrated acid and at or above the point at which oxidation and/or carbonization of the organic contaminants of the acid takes place, this point normally being between about and 185 C. Within this temperature range introduction of dilute acid into the concentrator does not cause undue foaming, provided that the introduction be so regular and continuous as to permit the foam-forming material to be decomposed in a short time. Irregular or too rapid feeding causes an accumulation of foam-forming material and subsequent foaming yin the concentrator. Thus, residence time is also a factor in the intermediate concentration unit; it has been found preferable to use a concentrator of suflicient size and a feed rate such that an average residence time of the order of 11/2 to 3 hours in this unit is maintained. Temperature substantially over C. should preferably be avoided during this step to avoid loss of acid due to oxidation of organic and/or carbonaceous matter separating in the unit. Further, the :carbon separating during this stage has been found to be difficult to filter if temperaturesl appreciably in exces of 185 C. are utilized.

1n the separation unit 4 organic impurities which have been converted to an insoluble form in intermediate concentration unit 2 are removed from the acid by ltration, skimming after stratiflcation, centrifugation or other suitable methods. It having been found, surprisingly, that A these insoluble impurities" (principally'carbonl' contain as muchas timestheir weighto more sulfuric acid, apparently loosely boundchemically to the carbon, -a second"separationiunit'4d is preferabiy provided.' Thus, wheny filters are used as separation units; for example, acid leaving intermediate concentration unit 2 and-con-r` taining insoluble impurities is passed through separation unit 4 until the separation becomes inefcient due to the size of ther cake on the nlter; the acid stream is thereupon bypassed through separation unit 4a, theI filter cake in separation unit i meanwhile beingbackwashe'd with water to displace the sulfuric acid contained therein. The backwash'water, including the re covered acid, is returned to dilution and separation unit l. The two units 4 and la are thus used alternately vfor separation purposes and backwashed to recover the acid contained in the insoluble impurities, this acidbeing returned to the system in separation and dilution unit 1.

After removal of organic contaminants in separation unit 4 the acid is continuously passed into the final concentration unit 3,the acid Aleaving this unit being concentrated to about 92-95%. Further concentration with S03 in fortification unit 5 may be and is preferably carried out if th'e acid is to be re-used for alkylationpurposes.

As a result of the above described 2l-stage concentration method thel exit gases from intermediate 1concentrator unit 2', and, in certain instances from final concentrator unit 3`, will contain a sufficiently high concentration of SO2 to make the recovery thereof economicallyfeasible; These gases are therefore passed' to SO2 recovery and S03 production units 5 wherein the SO2 is oxidized or otherwise processed to produce S03, which in turn may be utilized for fortification purposes in fortification unit 6.

The advantage of prompt dilution of the acid is shown by the following results of treatment of spent sulfuric acid from the alkylation at about 5 C. of isobutane with normal butylene.

Each of the acids was concentrated by a threestage continuous process. Acid of about 99% concentration was recoveredas the'iinal product inboth cases. The product obtained'from the acid which had not been promptly diluted contained 1.05% of its carbon content before dilution while by prompt dilution this figurewas reduced to 0.4%. The loss of acid' inthe final concentration of the former was 5.74% compared with only 0.15% for the acid which hadbeen promptly diluted. Further loss of"a'cid',` which was not measured, took placein the acid not promptly diluted as evidenced by the presence of a'large amount of sulfur'dioxide therein prior to dilution.

Several particular advantages in'concentrating in the particular manner set forth herein may also be pointed out. For example, by concentrating in three stages, as described, foaming problems are completelyeliminated, the formationof Hfoam during concentration'- beingiherto- "6 ffe ione fof-'fthe maior problems 'in 'recovering spent alkylation acids. Further; 4'the 1 SO2 recovery system provided `permits commercial scale recovery and' utilization of this material, which,

in most existing acid concentration systems, is a primary disposal problem.

It is to be understood, of course, that the operating processes may be varied. Thus the process maybe carried out batchwise, intermittently or continuously. In View of the high heat of `dilution of concentrated sulfuric acid it is desirable to take suitable precautions to prevent local overheating as well as to'provide means for rapidly dissipatingl the h'eat generated in the dilution step. Still other variations in the process may be made and the invention is not limited to the details disclosed by way of illustration nor by any theory proposed in explanation of the improved results Which are obtained, but only by the terms of the accompanying claims.

The present application is a continuation of our copending application, Serial No. 385,900, filed March 29, 1941, and now forfeited.

We claim as our invention:

l. In :a process for recovering and reconcentrating spent sulfuric acid whichhas been used as an alkylation catalyst in a form suitable for re-use as an alkylationcatalyst, the steps comprisingdiluting said spent acid, substantially immediately after withdrawal of said acid from an alkylation system, to form two phases, a dilute aqueous acid phase and a hydrocarbon phase and thereafter concentrating said dilute aqueous acid phase in three stages, -a first stage wherein said dilute acid is concentrated at a temperature imn mediately below the foaming point of said acid, a second stage wherein said dilute acid is concentrated at a temperature above the foaming point of said dilute acid and at a temperature whereat organic contaminants remaining in said dilute acid are decomposed and thus rendered insoluble therein but below th'e temperature at which appreciable reaction takes place between the acid and organic contaminants rendered insoluble during said second concentration stage and a third stage wherein the acid is concentrated at a temperature corresponding approximately to the boiling point of sulfuric acid at the desired final concentration, the organic contaminants rendered insoluble in the'second stage being removed from said acid between the second and third stages.

2. In a process for recovering and reconcentrating spent sulfuric acid which has been used as an alkylation catalyst in a form suitable for re-use as an lalkylation catalyst, the steps Icomprising promptly diluting said spent acid with suiiicient water to cause formation of a hydrocarbon ph'ase and a phase containing aqueous sulfuric acid of40% to about 55% concentration at a temperature at which substantial reaction of said hydrocarbon and said acid is avoided, separating said hydrocarbon phase and said dilute acid phase, continuously feeding said dilute acid into aliirst bodyof sulfuric Iacid maintained within the approximate temperature range of C., continuously feeding acid from said first body of acid into a second body of acid maintained within the approximate temperature range of i60-185 C. whereupon organic contaminants remaining in said acidv are decomposed and thus rendered insoluble therein, separating' said insoluble organic -contaminants from said second body of Vacid and continuously vfeeding the acid separated fromv said "organic contaminants zinto a third body of acid maintained within the ap:- proximate temperature range of 21B-240 C.

3. In a method for reconcentrating dilute rsulfuric acid which has been used as an alkylation catalyst in a form suitable for re-use in an alkylation process, the steps comprising promptly diluting said spent acid with sufficient water to cause formation of a hydrocarbon phase and a phase containing dilute sulfuric acid of 40% to about 55% concentration at Aa. temperature at which substantial reaction between said hydrocarbon phase and said dilute acid phase is avoided, feeding said dilute acid into a preliminary concentration unit containing a body of acid maintained within the approximate temperature range of 1Z0-140 C., feeding acid from said preliminary concentration unit to an intermediate concentration unit containing a body of acid maintained within the approximate temperature range of 1GO-185 C. whereupon organic contaminants remaining in said acid are decomposed and thus rendered insoluble therein, feeding acid from said intermediate concentration unit to a final concentration unit containing a body of acid maintained within the approximate temperature range of 21S-240 C.,.the temperature of the body of acid in each of said units being maintained by blowing hot gases therethrough, insoluble material present in the acidleaving said intermediate concentration unit being separated from said acid before feeding said acid to the final concentration unit and recovering sulfur dioxide from the exit gases leaving said intermediate and final concentration units.

4. In a process for recovering and reconcentrating spent sulfur acid which has been used as an alkylation catalyst in a form suitable for reuse as an alkylation catalyst, the steps comprising promptly diluting said spent acid with sufficient water to cause formation of a hydrocarbon phase and a phase containing aqueous sulfuric acid of 20% to about 55% concentration at a temperature at which substantial reaction of said hydrocarbon and said acid is avoided, feeding said dilute acid into a preliminary concentrationunit containing a body of acid maintained Within the approximate temperature range of 1Z0-140 C., feeding acid from said preliminary concentration unit to an intermediate concentration unit containing a body of acid maintained within the approximate temperature range of 16C-185 C. whereupon organic contaminants remaining in said acid are rendered insoluble therein, feeding acid from said intermediate concentration unit to a final concentration unit containing a body of acid maintained within the approximate temperature range of ZIO-240 C., the temperature of the body of acid in each of said units being maintained by blowing hot gases, therethrough, insoluble material present in the acid leaving said intermediate concentration unit being separated from said acid before feeding said acid to the final concentration unit, feeding acid from said nal concentration unit to a fortification unit and therein fortifying said acid with sulfur trioxide, recovering sulfur dioxide from the exit gases leaving said intermediate and nal concentration units, processing saidl sulfur dioxide to form sulfur trioxide and supplying said sulfur trioxide to said fortification unit.

5. In a process for recovering and reconcentrating spent sulfuric acid which has been used as an alkylation catalyst in a form suitable for re-use as an alkylation catalyst, the steps comprising promptly diluting said spent acid with sufficient water to cause formation of a hydrd-l carbon phase andra phase containing aqueous sulfuric acid of 40% to about 55% concentration at a temperature at which substantial reaction of said hydrocarbon and said acid is avoided, separating said hydrocarbon phase and said dilute acid phase, continuously feeding said dilute acid into a first body of sulfuric acid maintained within the approximate temperature range of 1Z0-140 C., continuously feeding acid from said first body of acid into a second body of acid maintained within the approximate temperature range of i60-185 C. whereupon organic contaminants remaining in said acid are rendered insoluble therein, separating said insoluble organic contaminants from said second body of acid, water Washing said insoluble impurities to recover sulfuric acid retained therein, returning said recovered sulfuric acid to said dilute feed acid and continuously feeding the acid separated from said organic contaminants into a third body of acid maintained within the approximate temperature range of 210-240" C.

6. In a process for recovering and reconcentrating spent sulfuric acid which has been used as an alkylation catalyst in a form suitable for re-use as an alkylation catalyst, the steps comprising promptly diluting said spent acid with sufficient water to cause formation of a hydrocarbon phase and a phase containing aqueous sulfuric acid of 20% to about 55% concentration at a temperature at which substantial reaction of said hydrocarbon and said acid is avoided, feeding said dilute acid into a preliminary concentration unit containing a body of acid maintained within the approximate temperature range of -140 C., feeding acid from said Preliminary concentration unit to an intermediate concentr-ation unit containing a body of acid maintained within the approximate temperature range of 16.0-" C. whereupon organic contaminants remaining in said acid are rendered insoluble therein, feeding acid from said intermediate concentration unit to a nal concentration unit containing a body of acid maintained within the approximate temperature range of 210240 C., the temperature of the body of acid in each of said units being maintained by blowing hot gases therethrough, insoluble material present in the acid leaving said intermediate concentration unit being separated from said acid before feeding said acid to the final concentration unit, said separation being carried out in a ltration unit, said filtration unit being periodically backwashed with water to recover sulfuric acid retained in said insoluble material, said recovered sulfuric acid being returned to the system in said aforementioned dilute feed acid, feeding acid from said final concentration unit to a fortification unit and therein fortifying said acid with sulfur trioxide, recovering sulfur dioxide to form sulfur trioxide and supplying said sulfur trioxide to said fortification unit.

JOHANNES H. A. P. LANGEN VAN une VALK. JAN D. RUYS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,991,745 Hechenbleikner Feb. 19, 1935 2,111,920 Wells Mar. 22, 1938 2,287,732 Frey Jan. 23, 1942 Certiicate of Correction Patent No. 2,441,521. May 11, 1948. JOHANNES H. A. P.`LANGEN VAN DER VALK ET AL.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Column 7, line 36, claim 4, for the Word sulfur read sulfuric; and that the said Letters Patent should be read With this correction therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 3rd day of August, A. D. 1948.

THOMAS F. MURPHY,

Assistant Commissioner of Patents, 

